Radio-frequency electric field bonding apparatus



June 17, 1947. G, BRQWN Er AL 2,422,525

RADIO FREQUENCY ELECTRIC FIELD BONDING APPARATUS Filed July .31, 1942 Willi www Inventors now Bumm AMRuDoLP.

Gttorncg hunted Juas-11, 1947 RADIO-FREQUENCY BONDIN G Bierwirth, Haddon Delaware ELECTRIC FIELD APPARATUS George H. Brown, Haddonileld, and Rudolph A.

Heights, N. J Radio Corporation of America,

assimors to a corporation of Application July 31, 1942, Serial No. 453.134

9Clalms.

l This invention relates to heating apparatus employing high frequency electrical energy, and

more particularly to kheating apparatus of the type specied which is especially suited for use in Joining togetherv laminated dielectric materials by means of a thermoplastic or thermo-setting bonding agent.

In certain industrial applications, as in the manufacture of laminated wood structures wherein the laminations are glued together under the influence of heat or forming operation, it has been found necessary to temporarily join together the layers or laminations in order to maintain them as a unit prior to subjecting them to the treatment by which they become permanently set in the desired form. 'I'his is particularly true where the sheet laminations are large, as in the case of airplane bodies made from relatively thin and long laminations of wood or the like. In order to hold the laminations together as a unit prior to subjecting them to the setting treatment, it has been customary to join them at spaced points by means of staples or the like. These staples must, however, later be removed after the laminated structure has been set in the desired shape, as they may have a deleterious eifect on the structure, so that the staples not only constitute a complete waste insofar as the finished product is concerned, but also considerable time is wasted in removing them.

The primary object of our present invention is to provide an improved apparatus for effecting more or less temporary joints between the several layers of a laminated structure composed of dielectric materials which are to be bonded together and pressure in a molding by a bonding agent, which apparatus will be free from the aforementioned disadvantages.

More particularly, invention to provide an improved apparatus for joining together the layers of a laminated structure as aforesaid which will eliminate the need for extraneous joining materials and which will make use of only the materials entering into the final, composite structure.

it is an object of our present Another object of our present invention is .to

provide improved heating apparatus for simultaneously applying radio frequency heatingand pressure to small areas of dielectric laminations coated with thermoplastic or thermosetting glue for the purpose of securing the laminations to each other at those'areas.

Still another object of our present invention is to provide improved apparatus as aforesaid which can be applied to the laminated structure Abe obvious that a sort of from only one side thereof to eilect the desired result.

It is also an object of our presentinvention to provide improved heating apparatus as above described which is simple in construction, inexpensive in cost, and highly emcient in use.`

In accordance with this invention, coupling of the heating device to the glue is accomplished from one side of the sheet material by means of two electrodes one of which is annular in shape and the other of which is circular in cross-section and is 4concentric with the ilrst electrode. The circular, center electrode is suitably spaced from the annular electrode, and the two electrodes are so supported and related to each other that the center electrode may be caused to exert relatively great pressure on the material. The electric field set up between the two electrodes, being radial, is most highly concentrated at the tip of the center electrode, and the stray field, thus concentrated, is used to activate the glue. Since the pressure is greatest at the tip of the center electrode and most of the heat is developed under it, the laminations will be bonded together over an area which is substantially equal to the area of the tip of the center electrode,y Thus, it will spot welding results wherever the center electrode contacts the work. A plurality of such spot welds may be used to temporarily unite the sheet laminations for subsequent, further treatment which will unite the laminations permanently and set them in the desired shape or form.

'I'he novel features that We consider characteristic of our invention are set forth with particularity in the appendedclaims. The invention itself, however, both as to its organization and the method of operation, as well as additional objects and advantages thereof, will best be understood from the following description of twoV embodiments thereoLfWhen read in connection with the accompanying drawing, in which Figure 1 is a side elevation of one form of heating device constructed in accordance with our present invention,

Figure 2 is a bottom plan view thereof,

Figure 3 is a central, longitudinal, sectional view of another form of heating device constructed according to our present invention,

Figure 4 is a bottom plan view of the latter form of our invention,

Figure 5 is a fragmentary plan view of two sheets or laminations joined together in accordance with our present invention, and

Figure 6 is a sectional view taken on the line corresponding parts ing.

VI-VI of Figure and exaggerated somewhat as to thickness for the sake of clearness.

Referring in greater detail to the drawing, wherein similar reference characters designate throughout, there is shown, in Figs, 1 and 2, a supporting plate I of dielectric material to which is connected and from one side of which there extends a manipulating handle 3. Also' connected to the supporting member l and extending from the opposite side thereof are a pair of electrodes 5 and 1. The electrode 5 is rigid and terminates in a tip 5a which is circular in cross section. rIhe electrode 'i is made of a strip of material which is somewhat resilient and terminatesin a disc-like annular portion la. which surrounds and is concentric.with the tip 5a of the electrode 5, the tip 5a having an area which is a small fraction of the area of the annular portion 1a. Connection to a suitable source of radio frequency energy, such as an oscillation generator (not shown), may be made by a concentric line 9 in well known manner.

The electrode 'i is so set that normally the annular portion 'Ia thereof occupies a position slightly in advance of the electrode tip 5a. In applying the device to the outer surface of a pair of. sheet laminations I3 and I5 between the facing surfaces ofwhich is interposed a layer oi glue i'i, the annular electrode portion 1a is irst brought into engagement with the surface of one ci the sheets, for example, thesheet I3. When pressure is applied against the work through the manipulating handle 3, the electrode l yields until the tip 5a is also in engagement with the lamination i3. rIhe circuit may then be completed, as by a switch on the handle 3 (not shown), whereupon an electric field is set up between the electrodes 5a and 1a. This field includes a direct field component as well as a stray field component between the two electrodes, the elds being most highly concentrated at the electrode tip 5a by reason of the fact that it extends radially. The stray field component is availed of to energize or activate the glue or the like Il for the purpose of heating and thereby softening it, and, since the pressure per unit area is relatively great under the tip 5a, it is obvious that a bond will be readily effected over an area under and substantially equal to the cross-sectional area of the electrode tip 5a. A plurality of such bonding area-s I9 may be provided at spaced points over the laminations I3 and I5, and these will serve effectively to temporarily hold the sheets I3 and I5 together until they are permanently united.

In one construction according to the form oi our invention just previously described, the electrode 'I was made of one-eighth inch brass shaped as shown in Fig, 1, and the center electrode 5 was made of one-quarter inch brass rod tapered down to one-eighth inch at the tip 5a and rounded off at the tip to reduce the possibility of arcmade of a Bakelite block. This construction was employed to provide temporary joints between two sheets of mahogany Veneer one-thirty second inch thick, and each coated with a phenolic thermosetting glue on the facing surface thereof.

The device was connected to an oscillation generator which supplied energy at 16 inegacycles, and the power required was about 20 watts to heat the small areas I9 to approximately 240 F. in one second. Frequencies of from 5 megacycles up were also employed successfully.

The supporting plate or member I was In the form of our invention shown in Figs. 3 and 4, the heating device consists of a cylindrical, metal tube 2| which forms the outer conductor of a concentric line. The inner conductor consists of a coil 23 embedded in a layer of polystyrene 25 or other suitable dielectric which will maintain the conductors 2| and 23 in suitably spaced relation. The concentric line 2|, 23 is connected to a suitable oscillation generator through a flexible cable or the like 21.

The tubular conductor 2| is provided at its lower end with a radially inwardly extending, disc-like, annular terminal member 29 constituting the outer electrode corresponding to the electrode 1a of Fig. l. Spaced from and concentric with the electrode 29 is an inner electrode 3| which, like the electrode 5, terminates in a tip which is rounded off and has a circular cross-section. The electrode 3| has a shank surrounded by a coil spring 33 which is interposed between a shoulder 35 and the end of a tubular, conductive socket 31 fitted into a corresponding seat in the lower end of the spacer 25 and conductively coupled to the coil 23,

The spring 33 serves to normally project the electrode 3| to a position such that its tip is located slightly beyond the electrode 29. When the tip 3| is brought into engagement with the outer surface of the sheet I3 and pressure is applied thereto, the spring 33 yields and permits the annular electrode 29 also to be brought into engagement with the work surface. However, the pressure per unit area and the strength of the eieotric field are both greatest under the tip of the electrode 3|. Consequently, the small joints or spot welds I9 will result similarly to those obtained with the apparatus of Fig. l. The length of the concentric line 2|, 23 is preferably about a quarter wave length at the operating frequency, which may be from 30 to 40 megacycles. In this way, a low voltage may be supplied by the oscillator through the flexible cable 2'I to the upper end of the concentric line and, because the device represents a quarter wave length, a standing wave will be established which will result in a high voltage at the lower end of the line between the electrodes 29 and 3|.

Although we have shown and described but two embodiments of our invention, it will be obvious to those skilled in the art that many other forms thereof, as well as variations in the ones described, are possible. We, therefore, desire that our invention shall not be limited except insofar as is made necessary by the prior art and by the spirit of the appended claims.

We claim as our invention:

l. In heating apparatus employing high frequencyelectrical energy for activating a dielectric bonding adhesive interposed between two adjacent sheets of laminations, the combination of an outer, disc-like, annular electrode disposed in a plane, an inner electrode concentric with said outer electrode and spaced radially therefrom, the end of said inner electrode terminating at a point in proximity to said plane and said inner electrode having a cross sectional area which is small compared to that of said outer electrode, common supporting means for both said electrodes, said annular electrode having connection with said common supporting means only at at least a portion of its periphery, one of said electrodes normally extending beyond the other of said electrodes and being yielda-ble relative thereto whereby when said one electrode is brought up against the outer surface of one of said sheets and pressure is applied thereto, said one electrode will yield to permit also bringing said other electrode into engagement with said surface, and means connected to said electrodes for connecting said electrodes to a source of high. frequency electric energy to thereby establish between said electrodes a high frequency electric field having a stray component for activating said adhesive.

2. In heating apparatus employing high frequency electrical energy, the combination of a supporting element, a rigid electrode connected to said supporting element and terminating in a tip having a circular cross section, and a yieldable electrode also connected to said supporting element and terminating in an annulus which surrounds said tip in spaced relation thereto, said annulus being concentric with said tip and said tip having a cross sectional area which is small compared to the area of said annulus.

3. In heating apparatus employing high frequency electrical energy for activating a bonding adhesive interposed between two adjacent sheets of laminations, the combination of a supporting element, a rigid electrode extending from one side of said supporting member and terminating in a tip having a circular cross section, a yieldable electrode also extending from the same side of said supporting element and terminating in an annulus which surrounds said tip in spaced relation thereto, said annulus being concentric with said tip and said tip having a cross sectional area which is small compared to the area of said annulus, said annulus also normally occupying aplane somewhat beyond the extremity of said tip, and a handle extending from the opposite side of said supporting element for manipulating said apparatus whereby said annulus may be brought against the surface of one oi said sheets and, when pressure is applied thereto, said annulus will yield to permit said tip also coming into engagement with said surface.

4. In heating apparatus employing high frequency electrical energy for activating a bonding adhesive interposed between two adjacent sheets of laminations, the combination of a supporting element, a rigid electrode extending from one side of said supporting member and terminating in a tip having a circular cross section, a yieldable electrode also extending from the same side of said supporting element and terminating in an annulus which surrounds said tip in spaced relation thereto, said annulus rbeing concentric with said tip and said tip having a cross sectional area which is small compared to the area of said annulus, said annulus also normally occupying a plane somewhat beyond the extremity of said tip, a handle extending from the opposite side of said supporting element for manipulating said apparatus whereby said annulus may be brought against the surface oi' one of said sheets and. when pressure is applied thereto, said annulus will yield to permit said tip also coming into engagement with said surface, and means connected to said electrodes providing an external connection to a source of said energy, said energy being adapted to set up between said electrodes a stray electric field which is most highly concentrated at said tip and which is adapted to activate said bonding osent over substantially the area of said tip to thereby unite said sheets over an area substantially equal to that of said tip.

5. In heating apparatus employing high frcquency electrical energy, the combination of a conductive, tubular member constituting the outer conductor of a concentric line and terminating in a radially extending annulus constituting a rst electrode, a conductive element arranged within said tubular member and constituting the inner conductor of said line, and a second electrode connected to said conductive element, said second electrode terminating in a circular tip which is spaced from and is concentric with said annular electrode.

6. Heating apparatus according to claim 5 characterized in that said tip has a cross sectional area which is small compared to that of said annular electrode.

7. Heating apparatus according to claim 5 characterized in that one of said electrodes is yieldable relative to the other of said electrodes and normally extends therebeyond whereby, upon bringing said yieldable electrode against a work surface and applying pressure thereto, said yieldable electrode will yield to permit said other electrode also coming into engagement with said work surface.

8. Heating apparatus according to claim 5 characterized by the addition of yieldable coupling means between said second electrode and said inner conductor, said coupling means normally acting to project said second electrode to a, position such that the tip thereof extends beyond said annular electrode, said coupling means yielding under pressure when said tip is brought into engagement with a work surface to permit said annular electrode also to be brought into engagement with said work surface.

9. Heating apparatus according to claim 5 characterized in that said concentric line has a length approximately equal to one quarter of the wavelength of the frequency of said electrical energy whereby a standing wave may be set up in said line which has substantially maximum voltage at said electrodes.

GEORGE H. BROWN. RUDOLPH A. BIERWIR'I'H.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,522,188 Hull Jan. 6, 1926 2,222,615 Hart, Jr Nov. 26, 1940 2,263,681 Hart, Jr. Nov. 25, 1941 2,147,689 Chaffee Feb. 2l, 1939 2,308,043 Bierwlrth Jan. 12, 1943 2,317,281 Linquist Apr. 20, 1943 1,555,258 Allcutt Sept. 29, 1925 2,280,771 Dufour et al. Apr. 28, 1942 2,045,523 Fassler June 23, 1936 2,302,119 Hagedorn Nov. 17, 1942 2,145,724 Horsley Jan. 31, 1939- FOREIGN PATENTS Number Country Date 656,681 Germany Feb. 11, 1938 

